Gear oil is used in industrial applications as well moving equipment such as automobiles, tractors, and the like (collectively referred to as “equipment”). When in use in some applications, the gear oil is present as an oil film between the moving parts, e.g., traction drives. In traction drive applications, power is transmitted via the gear oil film. In some applications, e.g., a hypoid gear of final reduction gear, it is very desirable to form/retain a thick oil film between gears. Increased oil film thickness to a sufficient level can protect a friction surface from damages, greatly improving gear and/or bearing fatigue life and load resistance characteristics.
Traction coefficient is the force required to move a load, divided by the load. The coefficient number expresses the ease with which the lubricant film is sheared. It is desirable for gear oils to have a low traction coefficient as the lower the traction coefficient, the less energy is dissipated due to lubricant shearing.
Besides having a low traction coefficient, it is important for a gear oil to have a high pressure-viscosity coefficient. The pressure-viscosity coefficient (“PVC”) refers to the relationship between the load placed on the oil film (pressure) at the dynamic load zone and the thickness of the oil film (viscosity) at that load, when all other factors (material, temperature, geometry, speed, load) are constant. The pressure-viscosity coefficient of a gear oil is a fixed value for an oil film thickness in a given set of conditions (elastohydrodynamic regime, also known as an EHL or EHD regime) based on a mathematical estimation as noted in the American Gear Manufacturers Association (AGMA) Information Sheet AGMA 925-A03. It is desirable for gear oils to have a high PVC value.
In a number of patent publications and applications, i.e., US 2006/0289337, US2006/0201851, US2006/0016721, US2006/0016724, US2006/0076267, US2006/020185, US2006/013210, US2005/0241990, US2005/0077208, US2005/0139513, US2005/0139514, US2005/0133409, US2005/0133407, US2005/0261147, US2005/0261146, US2005/0261145, US2004/0159582, U.S. Pat. No. 7,018,525, U.S. Pat. No. 7,083,713, U.S. application Ser. Nos. 11/400,570, 11/535,165 and 11/613,936, which are incorporated herein by reference, an alternative hydrocarbon product, i.e., a Fischer Tropsch base oil is produced from a process in which the feed is a waxy feed recovered from a Fischer-Tropsch synthesis. The process comprises a complete or partial hydroisomerization dewaxing step, using a dual-functional catalyst or a catalyst that can isomerize paraffins selectively. Hydroisomerization dewaxing is achieved by contacting the waxy feed with a hydroisomerization catalyst in an isomerization zone under hydroisomerizing conditions.
The Fischer-Tropsch synthesis products can be obtained by well-known processes such as, for example, the commercial SASOL® Slurry Phase Fischer-Tropsch technology, the commercial SHELL® Middle Distillate Synthesis (SMDS) Process, or by the non-commercial EXXON® Advanced Gas Conversion (AGC-21) process. Details of these processes and others are described in, for example, EP-A-776959, EP-A-668342; U.S. Pat. Nos. 4,943,672, 5,059,299, 5,733,839, and RE39073; and US Published Application No. 2005/0227866, WO-A-9934917, WO-A-9920720 and WO-A-05107935. The Fischer-Tropsch synthesis product usually comprises hydrocarbons having 1 to 100, or even more than 100 carbon atoms, and typically includes paraffins, olefins and oxygenated products. Fischer Tropsch is a viable process to generate clean alternative hydrocarbon products.
There is a need for a gear oil composition containing alternative hydrocarbon products having a low traction coefficient, a high pressure-viscosity coefficient, and optimal film thickness properties.